Does anyone have any idea what the hell this means or what t cells are? "t cells that fight bacterial and viral infections" im clueless on this

When does dna replication(make a copy of itself)?

What causes an unsaturated fatty acid to have a different shape than a saturated fatty acid? o a. unsaturated fatty acids have more hydrogen atoms. o b. unsaturated fatty acids have double carbon bonds. o c. unsaturated fatty acids have more nitrogen atoms. o d. unsaturated fatty acids have single carbon bonds.

Of seawater increases with decrease in the temperature. therefore, the cold water sinks to the deeper layers at the bottom